In the case of on-board storage of hydrogen for vehicular applications, automobile manufacturers require lightweight, compact, safe, and cost-effective storage plus the ability to achieve a driving range of at least 300 miles. The 300-mile driving range requires 5-10 kg of usable hydrogen depending upon the size of the vehicle. Although various hydrogen storage technologies are presently available, none completely satisfies all of the auto industry requirements. In fact, finding a solution to the hydrogen storage problem is considered by many to be the foremost challenge for the hydrogen economy. If you're interested in learning more about hydrogen storage, please visit our Hydrogen Basics.

FSEC has long researched many different hydrogen storage techniques
and technologies in partnership with federal agencies. One important
project was the identification of borane class complexes and alkaline
earth metal halide ammoniates as hydrogen storage compounds for
vehicular applications. These storage results on complex chemical compounds
were shown to meet DOE’s storage goals and the research is still
of great interest to DOE. The research
projects listed below all focus on solving hydrogen storage issues.

Complex Hydrides for Hydrogen Storage

The objective of this research was to investigate complex hydrides for use as hydrogen storage materials. These compounds, sometimes referred to as chemical hydrides, were previously not known to be reversible. However, recent R&D has shown that sodium aluminum hydride, NaAlH4, can be reversibly dehydrided. This research involved the investigation of a series of complex hydrides of aluminum and/or boron, with large hydrogen contents, a minimum of 7.7% by mass. The purpose of these studies were to determine the fate of the catalytic additives in order to surmise the mechanism of the catalytic actions in order to evaluate and determine more promising catalysts. This project was funded by the U.S. Department of Energy.

Smart Porous Metal-Organic Frameworks (MOFs) for Hydrogen Storage

Synthesis of novel materials from molecular building blocks (MBBs) offers
an opportunity to address the vision of layered structures since new
nanostructures can be accessed via “bottom-up” approaches.
Recently, applications of rigid MBBs have led to the development of a
wide range of metal-organic frameworks with large accessible 3-D pores
decorated with adjustable periodic organic and inorganic moieties suitable
for hydrogen uptake. The project’s strategy and approach involves
the development of tunable porous metal-organic frameworks for H2 storage.
The results provide a basis for developing selected metal-organic frameworks
as high-capacity hydrogen storage materials for onsite H2 recovery, purification
and storage. This project was a cooperative effort with USF and was funded
by NASA.

LH2 Storage Tanks at KSC

The objective of this project is to develop a thermal model to examine
the thermal performance of the Pad B LH2 tank at KSC and measure
the experimental parameters that are needed for modeling of the
granular effects of using glass bubbles as tank insulation. A detailed
3-D model was developed to simulate thermal performance of the
tank with a void. The model was validated against measured data,
including boiloff rates, IR images, point temperature and heat flux measurements.
A parametric study was performed after validation to investigate
which solutions are feasible for future tank renovation. Preliminary
recommendations from thermal simulations were made to KSC. Experimental
data from 3M Corp were also sent to KSC to support their modeling
efforts. This
project was funded by NASA.

Evaluation of New Insulation Systems

Due to heat leaks, liquid hydrogen (LH2) in storage tanks can vaporize
and cause the tank to become over-pressurized. In order to reduce
the tank pressure, the vaporized hydrogen has to be released into
the atmosphere, therefore losing valuable hydrogen. The boil-off costs
NASA-KSC about $1 million annually. The main challenge, then, is keeping
heat leaks to a minimum in liquid hydrogen storage tanks. Insulation
systems are used to reduce heat leaks. The objectives of this project
were 1) Develop a basis for evaluating hydrogen storage insulation systems,
and 2) Evaluate innovative and state-of-the-art insulation systems used
in hydrogen storage to minimize heat leaks. The present study concentrated
on development of general equations of thermal conductivities for
different insulation systems at various temperatures and pressures. The
models were validated against measured data under LN2 conditions and
can be also expanded for use with LH2 boundaries. Evaluation was performed
using the developed model. The study found that combination of different
insulation materials and MLI has no benefit. The vacuum level is an important
factor for selecting insulation materials. This project was funded
by NASA.

Hydrogen Purification and Storage Using Lithium Borohydride

NASA-KSC currently has an 850,000 gal capacity liquid hydrogen (LH2) tank for each of its two shuttle launch pads. Current supply strategies are such that typically about 700,000 gal in each tank are on hand. The stated capacity of the space shuttle on-board LH2 tank is 385,000 gal, but when boil-off, launch scrubs, ancillary on-site uses, and space vehicle usage (fuel cell power) are taken into account, each launch consumes about 500,000 gal LH2. In other words, NASA currently keeps less than a single launch’s worth of excess H2 fuel capacity near each launch pad. Boil-off losses in each dewar simply while standing amounts to some 400-600 gal/day, or 183,000 gal/year. Thus it is problematic to store hydrogen on-site long-term in liquid form. Producing hydrogen on-site could solve many logistical problems. A remaining problem, however, is that NASA’s demand for H2 is dictated by its launch schedule, so that its daily consumption of H2 is quite irregular. For on-site production, one is faced with either: 1) moderating the H2 production rate at the local facility to match the launch schedule; 2) increase the on-site storage capacity for LH2 well above the current capacity; or 3) have some sort of H2 buffering or storage capacity between the production plant and the liquefaction plant. This project was funded by NASA.

Ammonia-Borane
Complexes for Hydrogen Storage

Ammonia borane (AB) complex is a chemical hydride that is stable in
air and water, and contains very high hydrogen content (19.6 wt%). Release
of hydrogen in the AB complex can occur by either thermolysis or
hydrolysis. Thermolysis
of AB generates, in addition to hydrogen, species such as borazine,
monomeric aminoborane, and diborane, among others that have adverse effect
on fuel cell operation. This work presented a new process for generating
hydrogen at near room temperatures by hydrolysis of AB complex
using small amounts of several platinum group metal catalysts. The
kinetics of the AB hydrolysis in the presence of K2Cl6Pt catalyst was
studied using in situ 11B-NMR spectroscopy. The GC/MS analysis
of the product gas showed that the amount of ammonia detected in the
reactor effluent was significantly less when phosphoric acid was used
as a sequestering agent. The report also presents the thermal properties
and conductivities of composites formed by mixing fine aluminum powder
with AB complex at temperatures in the range of 300-420K. This project
was funded by NASA.

Metal Hydrides for Hydrogen Separation, Recovery and Purification

The goal of this project is to develop technologies that are capable of selectively removing hydrogen from a hydrogen/helium stream in order to recover pure hydrogen and pure helium, and those capable of absorbing hydrogen from boil-off. It is also our goal to recommend technologies that we believe are appropriate for NASA’s use and that will be transparent to the mission of the Center.

The typical space shuttle launch from Kennedy Space Center requires the use of 483,000 gallons of hydrogen, of which 98,000 gallons are lost to boil-off. Additionally, over 75 million standard cubic feet per year of helium are lost from processes used for purging lines and systems that will or have contained liquid hydrogen. These huge quantities of hydrogen and helium represent a substantial financial investment that could be preserved with the use of the appropriate technologies.

The systems resulting from this study will allow NASA to save many dollars by recapturing hydrogen boil-off and recovering the helium purge gas. Preventing the escape of hydrogen boil-off will also greatly enhance the safety of liquid hydrogen transfer and storage operations. This project was funded by NASA.